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.TH MSGCTL 2 "Mar 22, 2004"
.SH NAME
msgctl \- message control operations
.SH SYNOPSIS
.LP
.nf
#include <sys/msg.h>

\fBint\fR \fBmsgctl\fR(\fBint\fR \fImsqid\fR, \fBint\fR \fIcmd\fR, \fBstruct msqid_ds *\fR\fIbuf\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBmsgctl()\fR function provides a variety of message control operations as
specified by \fIcmd\fR. The following \fIcmd\fRs are available:
.sp
.ne 2
.na
\fB\fBIPC_STAT\fR\fR
.ad
.RS 12n
Place the current value of each member of the data structure associated with
\fImsqid\fR into the structure pointed to by \fIbuf\fR. The contents of this
structure are defined in \fBIntro\fR(2).
.RE

.sp
.ne 2
.na
\fB\fBIPC_SET\fR\fR
.ad
.RS 12n
Set the value of the following members of the data structure associated with
\fImsqid\fR to the corresponding value found in the structure pointed to by
\fIbuf\fR:
.sp
.in +2
.nf
msg_perm.uid
msg_perm.gid
msg_perm.mode /* access permission bits only */
msg_qbytes
.fi
.in -2

This command can be executed only by a process that has either the
{\fBPRIV_IPC_OWNER\fR} privilege or an effective user \fBID\fR equal to the
value of \fBmsg_perm.cuid\fR or \fBmsg_perm.uid\fR in the data structure
associated with \fImsqid\fR. Only a process with the
{\fBPRIV_SYS_IPC_CONFIG\fR} privilege can raise the value of \fBmsg_qbytes\fR.
.RE

.sp
.ne 2
.na
\fB\fBIPC_RMID\fR\fR
.ad
.RS 12n
Remove the message queue identifier specified by \fImsqid\fR from the system
and destroy the message queue and data structure associated with it. This
\fIcmd\fR can only be executed by a process that has an effective user \fBID\fR
either with appropriate privileges asserted in the effective set or equal to
the value of \fBmsg_perm.cuid\fR or  \fBmsg_perm.uid\fR in the data structure
associated with \fImsqid\fR. The \fIbuf\fR argument is ignored.
.RE

.SH RETURN VALUES
.sp
.LP
Upon successful completion, \fBmsgctl()\fR returns \fB0\fR. Otherwise, it
returns \fB\(mi1\fR and sets \fBerrno\fR to indicate the error.
.SH ERRORS
.sp
.LP
The \fBmsgctl()\fR function will fail if:
.sp
.ne 2
.na
\fB\fBEACCES\fR\fR
.ad
.RS 13n
The \fIcmd\fR argument is \fBIPC_STAT\fR and operation permission is denied to
the calling process (see \fBIntro\fR(2)).
.RE

.sp
.ne 2
.na
\fB\fBEFAULT\fR\fR
.ad
.RS 13n
The \fIbuf\fR argument points to an illegal address.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 13n
The \fImsqid\fR argument is not a valid message queue identifier; or the
\fIcmd\fR argument is not a valid command or is \fBIPC_SET\fR and
\fBmsg_perm.uid\fR or \fBmsg_perm.gid\fR is not valid.
.RE

.sp
.ne 2
.na
\fB\fBEOVERFLOW\fR\fR
.ad
.RS 13n
The \fIcmd\fR argument is \fBIPC_STAT\fR and \fIuid\fR or \fIgid\fR is too
large to be stored in the structure pointed to by \fIbuf\fR.
.RE

.sp
.ne 2
.na
\fB\fBEPERM\fR\fR
.ad
.RS 13n
The \fIcmd\fR argument is \fBIPC_RMID\fR or \fBIPC_SET\fR, the
{\fBPRIV_SYS_IPC_OWNER\fR} privilege is not asserted in the effective set of
the calling process, and is not equal to the value of \fBmsg_perm.cuid\fR or
\fBmsg_perm.uid\fR in the data structure associated with \fImsqid\fR.
.sp
The \fIcmd\fR argument is \fBIPC_SET,\fR an attempt is being made to increase
to the value of \fBmsg_qbytes\fR, and the {\fBPRIV_SYS_IPC_CONFIG\fR} privilege
is not asserted in the effective set of the calling process.
.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
c | c
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Standard
.TE

.SH SEE ALSO
.sp
.LP
.BR Intro (2),
.BR msgget (2),
.BR msgrcv (2),
.BR msgsnd (2),
.BR attributes (7),
.BR privileges (7),
.BR standards (7)
